1. Field of the Invention
The present invention relates to an aperture fluorescent lamp manufacturing method, which is suitably used for manufacturing a relatively small-diameter aperture fluorescent lamp having an aperture portion opened for light projection in a part of a straight glass tube in the axial direction, a manufacturing method of a surface illuminator provided with an aperture fluorescent lamp, a relatively small-diameter aperture fluorescent lamp, a surface illuminator provided with an aperture fluorescent lamp, a liquid crystal display device provided with the surface illuminator, and an electronic device provided with the liquid crystal display device.
The present application claims priority of Japanese Patent Application No.2000-215239 filed on Jul. 14, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
Conventionally, an aperture fluorescent lamp has been available, which emits light in a concentrated manner from an opening potion (referred to as an aperture portion, hereinafter) for light projection provided in a part of a straight glass tube in the axial direction. This aperture fluorescent lamp has widely been used as a backlight source, for example, in a liquid crystal display device for OA (Office Automation) equipment. The aperture fluorescent lamp has also been used as a document illumination light source in a facsimile, a copying machine, or the like.
With regard to a method for manufacturing such an aperture fluorescent lamp, technologies that have been available include, for example, one disclosed in Japanese Patent Laid-open No. Hei 6-260088 for forming an aperture portion by using a method of scraping off a phosphor with a rod (referred to as a first conventional technology), and one disclosed in Japanese Patent Laid-open No. Hei 9-306427 for forming an aperture portion with a photo mask (referred to as a second conventional technology).
In the case of the first conventional technology, as shown in FIG. 30, first, a phosphor is coated on the inner surface of a cylindrical glass tube 101 having both ends opened to form a phosphor layer 102. Then, a metal rod 104 having a brush 103 on a tip portion containing a magnetic substance like that shown in FIG. 31 is inserted from one opening of the glass tube 101 as shown in FIG. 32, and guided by a magnet 105 from the outside of the glass tube 101. The brush 103 is moved in pressed state to the phosphor layer 102 to scrape off the phosphor in a predetermined region, thus forming an aperture portion 106 as shown in FIG. 33.
In the case of the second conventional technology, first, a mixture of a photo-curing resin and a phosphor is coated inside a glass tube. Then, a photo mask (not shown) is attached to a predetermined region, in which an aperture portion 106 is formed, and irradiated with ultraviolet rays. Then, the photo mask is removed, an insensitive portion is washed off with hot pure water, and then dried and subjected to heating and burning. Then, a phosphor layer 102 is formed on other than the aperture portion 106 as shown in FIG. 33.
In addition, in both ends of an aperture fluorescent lamp 107 manufactured in the foregoing manner, as shown in FIG. 34, positioning pieces 108 for aligning an orientation of the aperture portion 106 at backlight assembly are attached.
To manufacture, for example, a backlight 115 of a side-light type, by using the aperture fluorescent lamp 107 having such positioning pieces, as shown in FIGS. 35 and 36, by fitting each of the positioning pieces 108 in a groove of a reflector 109 groove-shaped in section for reflecting and guiding light emitted from the aperture fluorescent lamp 107 to a light guide plate 112, the aperture fluorescent lamp 107 is attached to the reflector 109. Then, the reflector 109 having the aperture fluorescent lamp 107 attached thereto is fixed onto a rear case 110. At this time, the aperture portion 106 is positioned to face a direction (horizontal direction in FIGS. 35 and 36) roughly parallel to the top surface of the rear case 110 as a casing.
On the rear case 110, a reflection sheet 111, the light guide plate 112, and an optical correction sheet 113 are sequentially laminated, and then covered with a center case 114, thus completing the backlight 115.
To manufacture a directly-below backlight 116 of a directly-below type by using aperture fluorescent lamps 107, as shown in FIG. 37B, a plurality of aperture fluorescent lamps 107, 107 . . . , are positioned and disposed on the bottom part of a reflection plate 117 such that the aperture portions 106 can face a direction (directly above in the drawing) vertical to a light emission surface. Above the aperture fluorescent lamps 107, 107 . . . , a diffusion plate 118 is attached for obtaining a surface light source by diffusing emitted or reflected light.
With regard to the method for manufacturing the aperture fluorescent lamp, in the case of the first conventional technology, to manufacture a relatively small-diameter aperture fluorescent lamp, the brush 103 and the metal rod 104 must be formed thin. However, if the metal rod 104 is formed thin, the metal rod 104 is fluttered or bent, damaging the phosphor layer 102 other than the aperture portion 106. Consequently, it is practically difficult to manufacture a small-diameter aperture fluorescent lamp having an inner diameter of 3 mm or less.
In addition, to manufacture an aperture fluorescent lamp having a long glass tube length, length of the metal rod 104 must be made long. Thus, the metal rod 104 is fluttered or bent, damaging the phosphor layer 102 other than the aperture portion 106. Consequently, it is also difficult to manufacture an aperture fluorescent lamp having the long glass tube length.
Therefore, in the backlight as a surface illuminator using the aperture fluorescent lamp manufactured by the foregoing method, for example, as shown in FIG. 36, the size of a housing part 109h (FIG. 36) of the aperture fluorescent lamp 107, which is formed by being surrounded with the rear case 110, cannot be reduced. In other words, a longitudinal width a0 including clearances b0 and c0 in upper and lower sides of the aperture fluorescent lamp 107 and a transverse width d0 cannot be reduced. In addition, a width e0, which is regulated by the transverse width d0, of a frame part of the center case 114 above the aperture fluorescent lamp 107 cannot be reduced. Consequently, it is impossible to reduce not only weight of the aperture fluorescent lamp 107 but also those of other members.
It can therefore be understood that there are difficulties of thinning, narrow frame formation, and weight reduction for the backlight using the aperture fluorescent lamp manufactured by the described manufacturing method.
Thus, there are also difficulties of thinning, narrow frame formation, and weight reduction for both of a liquid crystal display device using the backlight and an electronic device using such the liquid crystal display device.
In the case of the second conventional technology, in addition to mixture coating step, exposure, developing, and many other steps are necessary. Thus, much time, and labor must be expended, thereby causing an increase in cost.
Therefore, there are problems of high costs for the backlight 115 as a surface illuminator using the aperture fluorescent lamp 107 manufactured by the described manufacturing method, a liquid crystal display device using the backlight 115, and a device using such the liquid crystal display device.
In the foregoing positioning method of the aperture portion 106, the positioning pieces 108 as members dedicated for positioning are necessary in the manufacturing process of the aperture fluorescent lamp 107.
Thus, material and process costs are increased by attaching (adhering) of the positioning pieces 108, and there are difficulties of thinning, narrow frame formation, and weight reduction when the aperture fluorescent lamp 107 is incorporated in the backlight 115.
If the positioning pieces 108 are omitted, when the aperture fluorescent lamp 107 is attached to the reflector 109 or the center case 114, an assembling operator must check position of the aperture portion 106, and align its orientation, thus making positioning difficult. Since a member around the aperture fluorescent lamp 107 becomes to be a visual obstacle during orientation alignment, the aperture portion 106 cannot be correctly positioned, thus deteriorating yield.
In the case of the directly-below backlight 116 using the aperture fluorescent lamp 107, for example, in a direction (y axis direction in FIG. 37A) orthogonal to the axis of the aperture fluorescent lamp 107 in the upper surface (light emission surface) of the diffusion plate 118, luminance is highest in a position (Y=Y0 in FIG. 38) directly above the aperture fluorescent lamp 107, and the luminance is lowest near a position (Y=Ym) equidistant from the axes of the adjacent aperture fluorescent lamps 107 and 107, thus generating luminance uneveness.
Specifically, as shown in FIG. 38, compared with a distance L0 between the axis of the aperture fluorescent lamp 107 and a position Q0 (Y=Y0, and Z=Z0) directly above the aperture fluorescent lamp 107 in the backside of the diffusion plate 118, a distance Lm between the axis of the aperture fluorescent lamp 107 and a position Qm (Y=Ym, and Z=Z0) equidistant from the adjacent aperture fluorescent lamps 107 and 107 in the backside of the diffusion plate 118 is longer. Light is diffused and attenuated by an amount equal to such a difference in optical path lengths, making dark a part near the position Qm. Further, near the position Qm, light is obliquely directed from the aperture fluorescent lamp 107. Thus, the component of a light intensity in a direction (Z axis direction) vertical to the light emission surface of the light diffusion plate 118 becomes smaller than that of a light intensity in the position Q0 directly above the aperture fluorescent lamp 107.
Therefore, because of the directional characteristic (relation between the direction of radiation and luminance) of the aperture fluorescent lamp 107, a part directly above the aperture fluorescent lamp becomes bright, and the middle part equidistant from the adjacent aperture fluorescent lamps 107 and 107 becomes dark. As shown in FIG. 37A, the luminance F of light emitted from the diffusion plate 118 is changed in a wave shape in the Y-axis direction of the light emission surface. Consequently, luminance uniformity is deteriorated.
The above problem occurs even when a general lamp other than the aperture fluorescent lamp is used.
Thus, in the conventional art, as shown in FIG. 37B, by setting the distance L0 between the aperture fluorescent lamp 107 and the diffusion plate 118 to be sufficiently long (for example, L0=13 mm to 15 mm), and diffusing light at the diffusion plate 118, luminance uniformity must be adjusted to a level at which the backlight 116 can be used as a product. Consequently, the distance L0 cannot be set equal to a predetermined value or lower.
It can therefore be understood that there are difficulties of thinning and weight reduction in the case of the directly-below backlight 116.